1. Field of the Invention
The present invention relates to a picture coding and decoding technique used to compress and expand a picture signal, and more particularly, to a technique by which to compress and expand picture data, which is buffered in a frame memory, when the picture signal is processed between frames.
2. Description of the Related Art
When an image or picture processing, such as the scaling or frame interpolation, is carried out, frame images or pictures need to be temporarily saved in a frame memory. In recent years, the images and pictures having high resolution are on the increase. This entails a rise in the clock rate, an increase in the number of terminals, an increase in memory capacity and so forth to transfer the high-resolution pictures between an arithmetic circuit and the frame memory. Thus a picture compression technology to reduce the transmission quantity of picture data in a system is in demand. Since such a picture compression technology aims to reduce the circuit scale and load within the system, it is required that the pictures be compressed in a simple manner and at a low load and, at the same time, the image degradation be suppressed to the minimum.
One of such methods for compressing the picture signal is a method where the error between a pixel of interest and locally-decoded pixels surrounding the pixel of interest is coded. In this method, a pixel most approximate to the pixel of interest among the neighboring pixels of the pixel of interest is selected, so that the prediction error value can be minimized. Proposed is a method where the pixel most approximate to the pixel of interest is estimated from a relation between the value of a pixel located one line above the pixel of interest and the locally decoded values of its surrounding pixels (see Reference (1) in the following Related Art List). Estimating a prediction direction by the use of the pixel one line above increases the time required to determine the prediction direction. As a result, an increase in the circuit scale can be suppressed.